Bug fix: When adjusting altitude, RTL then land will fail unless this var is reset to false.

ArduCopter/system.pde

@@ -400,6 +400,7 @@ static void set_mode(byte mode)
 
 	// clearing value used to force the copter down in landing mode
 	landing_boost = 0;
+	reset_throttle_flag = false;
 
 	// do we want to come to a stop or pass a WP?
 	slow_wp = false;